Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/17/1997
Publication Date: N/A
Interpretive Summary: The young seedlings of the cole crops broccoli, cauliflower, cabbage and collard are susceptible to a fungal disease called wirestem that attacks and rots the seedling roots and stems. This disease can kill the seedlings or damage the stem so that the plant remains stunted and does not produce a harvestable vegetable, consequently reducing crop yields. This research was undertaken to determine if different varieties of cole crops respond differently when attacked by the wirestem disease. Our ultimate goal is to identify varieties that are more resistant to wirestem that a farmer might grow to prevent losses due to a likely outbreak of the disease. Our results showed that a collard variety named 'Blue Max' was always more resistant to wirestem than other varieties and two cauliflowers, 'Snowcone' and 'Snowcrown' were always severely damaged by the disease. These results do indicate that a farmer should be able to minimize crop losses due to wirestem and increase the profitability of cole crop production by choosing a variety that shows some level of resistance. This information also provides a basis for us and other plant scientists to use in conducting further tests of cole crops to discover better levels of resistance than we have currently observed and to conduct a systematic effort to increase wirestem resistance through breeding.
Technical Abstract: Growth room and field experiments were conducted to develop methods to study resistance in Brassica oleracea crops to Rhizoctonia solani, causal agent of wirestem. Seedlings of 12 cultivars (three each of broccoli, cauliflower, cabbage, and collard) at the four- to five-leaf stage were transplanted to a growth room and covered with steamed soil infested with cornmeal-sand cultures or sclerotia or to fumigated field plots infested with sclerotia. Percentage healthy, diseased, and dead plants was assessed every 3 to 5 days for 2 weeks in the growth room and for 3 weeks in field trials. At harvest, plants were rated for wirestem severity. Wirestem incidence stabilized within 10 to 14 days after inoculation. Percent healthy and surviving (healthy plus diseased) plants, area under the disease progress curve (AUDPC), and wirestem severity all separated the most susceptible from partially resistant cultivars. Wirestem severity and dAUDPC were always negatively and significantly correlated with percent healthy plants. Although genotype by environment interactions were observed, the cauliflower cultivars Snowcone and Snowcrown were severely diseased in all experiments, while Blue Max collard was always significantly less diseased.